Toy Models for Galaxy Formation versus Simulations

We describe simple useful toy models for key processes of galaxy formation in its most active phase, at z > 1, and test the approximate expressions against the typical behaviour in a suite of high-resolution hydro-cosmological simulations of massive galaxies at z = 4-1. We address in particular the evolution of (a) the total mass inflow rate from the cosmic web into galactic haloes based on the EPS approximation, (b) the penetration of baryonic streams into the inner galaxy, (c) the disc size, (d) the implied steady-state gas content and star-formation rate (SFR) in the galaxy subject to mass conservation and a universal star-formation law, (e) the inflow rate within the disc to a central bulge and black hole as derived using energy conservation and self-regulated Q ~ 1 violent disc instability (VDI), and (f) the implied steady state in the disc and bulge. The toy models provide useful approximations for the behaviour of the simulated galaxies. We find that (a) the inflow rate is proportional to mass and to (1+z)^5/2, (b) the penetration to the inner halo is ~50% at z = 4-2, (c) the disc radius is ~5% of the virial radius, (d) the galaxies reach a steady state with the SFR following the accretion rate into the galaxy, (e) there is an intense gas inflow through the disc, comparable to the SFR, following the predictions of VDI, and (f) the galaxies approach a steady state with the bulge mass comparable to the disc mass, where the draining of gas by SFR, outflows and disc inflows is replenished by fresh accretion. Given the agreement with simulations, these toy models are useful for understanding the complex phenomena in simple terms and for back-of-the-envelope predictions.Comment: Resubmitted to MNRAS after responding to referee's comments; Revised figure

Gravity-driven Lyα blobs from cold streams into galaxies

We use high-resolution cosmological hydrodynamical adaptive mesh refinement (AMR) simulations to predict the characteristics of Lyα emission from the cold gas streams that fed galaxies in massive haloes at high redshift. The Lyα luminosity in our simulations is powered by the release of gravitational energy as gas flows from the intergalactic medium into the halo potential wells. The ultraviolet UV background contributes only <20 per cent to the gas heating. The Lyα emissivity is due primarily to electron-impact excitation cooling radiation in gas at ∼2 × 104 K. We calculate the Lyα emissivities assuming collisional ionization equilibrium at all gas temperatures. The simulated streams are self-shielded against the UV background, so photoionization and recombination contribute negligibly to the Lyα line formation. We produce theoretical maps of the Lyα surface brightnesses, assuming that ∼85 per cent of the Lyα photons are directly observable. We do not consider transfer of the Lyα radiation, nor do we include the possible effects of internal sources of photoionization such as star-forming regions. Dust absorption is expected to obscure a small fraction of the luminosity in the streams. We find that typical haloes of mass Mv∼ 1012-1013 M☉ at z∼ 3 emit as Lyα blobs (LABs) with luminosities 1043-1044 erg s−1. Most of the Lyα comes from the extended (50-100 kpc) narrow, partly clumpy, inflowing, cold streams of (1-5) × 104 K that feed the growing galaxies. The predicted LAB morphology is therefore irregular, with dense clumps and elongated extensions. The integrated area contained within surface brightness isophotes of 2 × 10−18 erg s−1 cm−2 arcsec−2 is ∼2-100 arcsec2, consistent with observations. The linewidth is expected to range from 102 to more than 103 km s−1 with a large variance. The typical Lyα surface brightness profile is ∝r−1.2 where r is the distance from the halo centre. Our simulated LABs are similar in luminosity, morphology and extent to the observed LABs, with distinct kinematic features. The predicted Lyα luminosity function is consistent with observations, and the predicted areas and linewidths roughly recover the observed scaling relations. This mechanism for producing LABs appears inevitable in many high-z galaxies, though it may work in parallel with other mechanisms. Some of the LABs may thus be regarded as direct detections of the cold streams that drove galaxy evolution at high

CGM properties in VELA and NIHAO simulations; the OVI ionization mechanism: dependence on redshift, halo mass and radius

We study the components of cool and warm/hot gas in the circumgalactic medium (CGM) of simulated galaxies and address the relative production of OVI by photoionization versus collisional ionization, as a function of halo mass, redshift, and distance from the galaxy halo center. This is done utilizing two different suites of zoom-in hydro-cosmological simulations, VELA (6 halos; $z>1$) and NIHAO (18 halos; to $z=0$), which provide a broad theoretical basis because they use different codes and physical recipes for star formation and feedback. In all halos studied in this work, we find that collisional ionization by thermal electrons dominates at high redshift, while photoionization of cool or warm gas by the metagalactic radiation takes over near $z\sim2$. In halos of $\sim 10^{12}M_{\odot}$ and above, collisions become important again at $z<0.5$, while photoionization remains significant down to $z=0$ for less massive halos. In halos with $M_{\textrm v}>3\times10^{11}~M_{\odot}$, at $z\sim 0$ most of the photoionized OVI is in a warm, not cool, gas phase ($T\lesssim 3\times 10^5$~K). We also find that collisions are dominant in the central regions of halos, while photoionization is more significant at the outskirts, around $R_{\textrm v}$, even in massive halos. This too may be explained by the presence of warm gas or, in lower mass halos, by cool gas inflows

Gravity-driven Lyman-alpha blobs from cold streams into galaxies

We use high-resolution cosmological hydrodynamical AMR simulations to predict the characteristics of La emission from the cold gas streams that fed galaxies in massive haloes at high redshift. The La luminosity in our simulations is powered by the release of gravitational energy as gas flows from the intergalactic medium into the halo potential wells. The UV background contributes only <20% to the gas heating. The La emissivity is due primarily to electron-impact excitation cooling radiation in gas ~2x10^4K. We calculate the La emissivities assuming collisional ionisation equilibrium (CIE) at all gas temperatures. The simulated streams are self-shielded against the UV background, so photoionisation and recombination contribute negligibly to the La line formation. We produce theoretical maps of the La surface brightnesses, assuming that ~85% of the La photons are directly observable. We find that typical haloes of mass Mv~10^12-13 Msun at z~3 emit as La blobs (LABs) with luminosities 10^43-44 erg/s. Most of the La comes from the extended narrow, partly clumpy, inflowing, cold streams that feed the growing galaxies. The predicted LAB morphology is therefore irregular, with dense clumps and elongated extensions. The linewidth is expected to range from 10^2 to more than 10^3 km/s with a large variance. The typical La surface brightness profile is proportional to r^-1.2 where r is the distance from the halo centre. Our simulated LABs are similar in luminosity, morphology and extent to the observed LABs, with distinct kinematic features. The predicted La luminosity function is consistent with observations, and the predicted areas and linewidths roughly recover the observed scaling relations. This mechanism for producing LABs appears inevitable in many high-z galaxies. Some of the LABs may thus be regarded as direct detections of the cold streams that drove galaxy evolution at high z.Comment: 21 pages, 20 figures, final version accepted for publication in MNRA

Short-lived star-forming giant clumps in cosmological simulations of z~2 disks

Many observed massive star-forming z\approx2 galaxies are large disks that exhibit irregular morphologies, with \sim1kpc, \sim10^(8-10)Msun clumps. We present the largest sample to date of high-resolution cosmological SPH simulations that zoom-in on the formation of individual M*\sim10^(10.5)Msun galaxies in \sim10^(12)Msun halos at z\approx2. Our code includes strong stellar feedback parameterized as momentum-driven galactic winds. This model reproduces many characteristic features of this observed class of galaxies, such as their clumpy morphologies, smooth and monotonic velocity gradients, high gas fractions (f_g\sim50%) and high specific star-formation rates (\gtrsim1Gyr^(-1)). In accord with recent models, giant clumps (Mclump\sim(5x10^8-10^9)Msun) form in-situ via gravitational instabilities. However, the galactic winds are critical for their subsequent evolution. The giant clumps we obtain are short-lived and are disrupted by wind-driven mass loss. They do not virialise or migrate to the galaxy centers as suggested in recent work neglecting strong winds. By phenomenologically implementing the winds that are observed from high-redshift galaxies and in particular from individual clumps, our simulations reproduce well new observational constraints on clump kinematics and clump ages. In particular, the observation that older clumps appear closer to their galaxy centers is reproduced in our simulations, as a result of inside-out formation of the disks rather than inward clump migration.Comment: 11 pages, 6 figures, 1 table. Accepted for publication in the Astrophysical Journa

Geometry of Star-Forming Galaxies from SDSS, 3D-HST and CANDELS

We determine the intrinsic, 3-dimensional shape distribution of star-forming galaxies at 0<z<2.5, as inferred from their observed projected axis ratios. In the present-day universe star-forming galaxies of all masses 1e9 - 1e11 Msol are predominantly thin, nearly oblate disks, in line with previous studies. We now extend this to higher redshifts, and find that among massive galaxies (M* > 1e10 Msol) disks are the most common geometric shape at all z < 2. Lower-mass galaxies at z>1 possess a broad range of geometric shapes: the fraction of elongated (prolate) galaxies increases toward higher redshifts and lower masses. Galaxies with stellar mass 1e9 Msol (1e10 Msol) are a mix of roughly equal numbers of elongated and disk galaxies at z~1 (z~2). This suggests that galaxies in this mass range do not yet have disks that are sustained over many orbital periods, implying that galaxies with present-day stellar mass comparable to that of the Milky Way typically first formed such sustained stellar disks at redshift z~1.5-2. Combined with constraints on the evolution of the star formation rate density and the distribution of star formation over galaxies with different masses, our findings imply that, averaged over cosmic time, the majority of stars formed in disks.Comment: Published in ApJ Letter

Keck-I MOSFIRE spectroscopy of compact star-forming galaxies at z≳\gtrsim2: High velocity dispersions in progenitors of compact quiescent galaxies

We present Keck-I MOSFIRE near-infrared spectroscopy for a sample of 13 compact star-forming galaxies (SFGs) at redshift $2\leq z \leq2.5$ with star formation rates of SFR$\sim$100M$_{\odot}$ y$^{-1}$ and masses of log(M/M$_{\odot}$)$\sim10.8$. Their high integrated gas velocity dispersions of $\sigma_{\rm{int}}$=230$^{+40}_{-30}$ km s$^{-1}$, as measured from emission lines of H$_{\alpha}$ and [OIII], and the resultant M$_{\star}-\sigma_{\rm{int}}$ relation and M$_{\star}$$-$M$_{\rm{dyn}}$ all match well to those of compact quiescent galaxies at $z\sim2$, as measured from stellar absorption lines. Since log(M$_{\star}$/M$_{\rm{dyn}}$)$=-0.06\pm0.2$ dex, these compact SFGs appear to be dynamically relaxed and more evolved, i.e., more depleted in gas and dark matter ($<$13$^{+17}_{-13}$\%) than their non-compact SFG counterparts at the same epoch. Without infusion of external gas, depletion timescales are short, less than $\sim$300 Myr. This discovery adds another link to our new dynamical chain of evidence that compact SFGs at $z\gtrsim2$ are already losing gas to become the immediate progenitors of compact quiescent galaxies by $z\sim2$.Comment: 12 pages, 7 figures, submitted to Ap

Cognitive Effects of Combined Amisulpride and Quetiapine Treatment in Patients With Refractory Schizophrenia: A Naturalistic, Prospective Study.

Background: There are different treatment options, but little support of evidence in the treatment of patients with resistant schizophrenia. In this study we used antipsychotic polypharmacy (AP) comprising 1200 mg of amisulpride and 600 mg of quetiapine, using neurocognitive evaluations to measure clinical change. Study Question: The AP of amisulpride and quetiapine implicará una mejoría clínica en pacientes with resistant schizophrenia que reflejará especialmente en una mejoría cognitiva. Study Design: Naturalistic and prospective study. 26 patients with no biological response to medication, high social maladjustment, a long history of the disease, to whom Kane's and Brenner's criteria for treatment-resistant schizophrenia were applied and assessed by a battery of neurocognitive evaluations desde a pre-treatment baseline y a los six months treatment. Measures and Outcomes: La mejoría cognitiva implicara una mejora significativa in the cognitive test: Stroop test, WAIS Coding Subtest, Continuous Trail Making Test (CTMT) desde la línea base y los 6 meses de tratamiento. También implicará mejoría en las escalas de Calgary Depression Scale (CDS), Simpson-Angus Scale (SAS) and a Visual Analogue Scale (EVA) con las que fueron evaluados en línea base, a los 3 meses y a los 6 meses. Results: Subjects, after six months treatment with amisulpride and quetiapine, did statistically significant difference in the assessed areas: WAIS Coding Subtest (P <0.001), CTMT A & B (CTMTA P< 0,034; CTMTB P< 0,000) and in Stroop tests: Word (P< 0,001), word-color (P< 0,007) and interference (P< 0,039). Furthermore they showed a statistically significant difference in CDS (P< 0,002), SAS (P< 0,019), and EVA (P < 0.001). Conclusion: The results of this report show a cognitive and clinical improvement in refractory patients after the administration of amisulpride and quetiapine.pre-print523 K